Electric heater



Sept. 2 19204.

D. E. SHAW ET AL LECTRIC HEATER Fnled Dec. 2,9 1920 2 Sheets-Sheet l l a l 1 @ooo G C Sept. z, 1924. Y f "1,507,005 D. E.l 'SHAW ET AL l ELECTRIC HEATER Filed Dec. 29 1920 2 Sheets-Sheet 2 Patented Sept. y 2, 1924.

UNITED STATES PATENT OFFICE.

DAVID E.' SHAW AND HAROLD ICHOLS SHAW, OF MILWAUKEE, WISCONSIN;l SAID .SDA'V'JIDv E. SHAW ASSIGNOR TO SAU) HAROLD N. SHAW.

ELECTRIC HEATER.

Application led December 29, 1920. Serial No. 433,868.

To all whom. t may cof/wem.:

Be it known that we, DAVID E. SHAW and HAROLD N. SHAW, citizens of the United States, and residents of Milwaukee, in the 6 county of Milwaukee and State of Wisconsin, have invented new and useful Improvements in Electric Heaters, of which the following is a description, reference being had to the accompanyingA drawings, which are a part of this specification.

This invention relates to certain new and useful improvements in electric heaters.

It is one of the objects of the present invention to provide a device of the class described in which a current is caused to i'low in a container or other object to be heated to raise the temperature thereof.

Another object of this invention is v to provide a heating device in which a primary coil and a secondary circuit are linked by a magnetic circuit, to produce heat in the secondary circuit by electric currents included therein; the secondary, in the event the element is used in connection with a cooking utensil, being preferably made integral with the utensil.

Another object of this invention is to provided a heating device in which the heating element is made of a metal. having af high temperature coefficient .of resistance, so that the heat developed in the latter causes bot-h its temperature and resistance to rise, .thereby decreasing the current consumed by the heater, Awhich latter decrease in current can be made to operate ya switch which changes the power consumed by the heater,v

when any desired temperature is reached by the heating element.

A further object of this invention is to provide a heating element of the class described so constructed and designed that any hum or noise whatsoever, due to vibration of the parts, is reduced to a minimum, if not eliminated altogether.

A further object of, this invention is to provide afheating device 'of .the class described which operates with a high power factor. l

A further object of this invention is to provide a heating device of the class described having a high and a low section in the primary coil, the high coil being con, nectible with the circuit to initially heat conducted to the heating element and uti-I lized, thus making possible an eiciency of 100%, and also making practical a Solid magnetic circuit and a light weight primary coil.

A further object of this vinvention is to provide a heating device of the class described including a high and a low coil and means for automatically disconnecting the I high coil and connecting the low coil in series with the same when the temperature of the heating element proper reaches the desired degree.

A further object of this invention is to provide a heating deviceA of .the class described, which, while especially designed for use in heating a utensil or other object, may

be utilized independently as a stove, or in any manner in which the same will perform the desired functions.

A further object of this invention is to make a heating element which will not burn out since it operates at low temperature.

A still further object of this invention is to provide a heating device of the class dgscribed, which heats quickly with a low temperature difference due to direct contact between heating element and substance lto be heated. v

A still further object 'of this invention is to provide a device of the class described in which the magnetic circuit is wholly outsidev of the container or completely covered by the working surface of the heating element.

With the aboveand other objects in viewl such changes in the precise embodiment of- Y sof between the succeeding turns of wire. The

the hereindisclosed invention may be made as come within the scope of the claims.

1n the accompanying drawings, we have illustrated one complete example of the physical embodiment of our invention constructed according to the best mode we have so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a side view of a cooking utensil equipped with our invention, parts .thereof being broken away and in section to illustrate structural details;

Figure 2 is a fragmentary view part in section and part in elevation taken on the plane of the line 2 2 of Figure 1;

Figure 3 is a fragmentary view illustrating the improved switchconstruction for connecting and disconnecting the high and low coils, part of the switch blade guide being broken away;

Figure 4 is a diagrammatic view illustrating the several complete circuits of the electrical heating device;

Figure 5 is a fragmentary sectional View taken through one of the spokes of lthe star shaped member forming the magnetic circuit, said view being taken on the line 5-5 of Figure 2;. and Figure 6 is an enlarged detail sectional view taken transversely through the core of theautomatic control coil on the plane of the line 6--6 of Figure 3, and

Fig.'7 is a fragmentary detail view of the spoked cover.

Referring now more particularly to the accompanying drawings, in which like numerals designate like parts throughout the several views.:

The numeral 10 designates the hub of a s tar-shaped-member having radiating arms 11, the outer ends of which are struck-'downwardly to form depending legs 12, and thus form part of the magnetic circuit. lVhile in this design the magnetic circuit is starshaped, it may be drum-shaped and completely surround and incase the coils within itself or be of any design between these two extremes.V The star-shaped member is preferably cast or otherwise formed of iron or other magnetic material and forms part of the magnetic circuit of the heater. Wound l' about the hub 10 in the space between it and the depending legs 12, is a low coil 13 and a high coil 14. These coils are constructed of wire which is asbestos covered,

lsuch covering being bothan electrical insulating and heeft vvresisting' material, but

j Amay be of any material having these properties or be insulated by allowing air space vcoils 13 and 14 form the. primary coils of the transformer-and `are connected with a source ,of electrical supply in .the manner stance, by the bottom 15 of a vessel 16 and projections therefrom of aluminum or other electrical conductor metal.

The bottom 15 of the vessel 16 has pairs j manner just described, the spokes may be cast therein as will be readily apparent to those skilled in the art to which an invention of this' character appertains. Current distributing lugs or' filling portions 19l are formed on the underside of the `vessel bottom 15 intermediate each adjacent pair of flanges 17, to make the resistance of the secondary circuit the same at the outerA periphery as at the inner periphery and so keep the current the same in all parts, said lugs having a spacebetween the side walls thereof and the adjacent flanges 17 as best shown in Figures 2 `and 5. yLugs 19 also make the resistance o f the part of the secondary circuit through. the lugs much less than the resistance of the path. over the members 11 through 'the bottom of the utensil. This causes most of the secondary current to flow through lugs 19 and flanges 17, which areclose to the primary coil and so have a low leakage reactance, and through the part of the bottom of the utensil between them, rather than through flanges 17 and around the members 11 through the part of the bottom of the utensil 15 over the latter, which is a path of high rea'ctance. This construction causes the device to operate at a high power factor.

It is evident that side member 22, hereinafter described, could also be madepart of the-secondary circuit and a heating element by extending around members 12, flanges similar to flanges 17 and adding lugs between said flanges similar to lugs 19. heating element could also befiXed to the bottom in' a lsimilar manner. Instead of using lugs 19, flanges 17 could be arranged to join onto 15 or 22 close together at all points, i. e. on either side of where the center of,19 was. With this construction and inthe caseof the flanges joining onto 15, the flanges 17 would be made thicker as the distance from the center would be increased, so as to keepthe resistance of the second.-

ary circuit about the same at all diameters.

loc

After the heating element has been fixed in place incasing' the magnetic circuit, the primary coils 13 andlfi are then fixed in place and spoked cover 20, of a size to `have a tight"l fit.k between the lower ends of the '.hub 10`a1id `depending.. legs\ 12, is'placed in position land forced against the coils under pressure t firmly secure vthe-same in thel the magnetic circuit and the primary coils space between the casing 2 with asbestos or 'may be termed a shunt solenoid 32, a series solenoid.

into close relation with the secondary or heating element, so that the latter conducts away the heat developed in the solid magnetic circuit and lthe primary coils, thus utilizing all the heat developed in the device, and making `practical the solid magne'tlic circuit and a reasonably light primary co1 The underside of the vessel 16 is provided with an annular side depending wall 22 which extends the entire length of the legs 12 to form a chamber or compartment in which the various parts of the heating device are incased and protected from wa- Jfer. rlhe upper end of the utensil 16 is directed laterally as at 23, and then downwardly, as at 24. the portion 24 thereof being annularly channeled, as at 25, to receive the upper end 26 of an outer protecting casing 27 in which the entire device is concealed. The roll 26 of the casing 27 is secured in place by suitable fastening screws 28 in the manner illustrated in Figure 1, and the inner wall defining. the channel 25 is longer than the outer one so that in the event that the utensil should be turned upside down and water should be in the channel, none will ass into the and utensil 16 in the event that the joint between said -roll 26 and depending` portion 24 of the vesselis not water-tight The space between the vessel 16 and casing 27 is filled any other heat insulating material, and the bottom of the heating element is separated from the control coils by an asbestos board or the like 29 which is secured in place by a fastening screw 30. The space between the board 29 andcasing 27 has two axially alined solenoids 31 and 32 secured to the board 29 which form a part of the automatic control device to be later described, the solenoid 31 being what solenoid and the The vessel 16 is adapted to receive readily removable steamer compartments 33 provided with a cover 34, and the walls of the .compartments 33 are perforated, as at 35,

the perforations beginning at a point spaced above the bottom of the compartments so that steam generated by the contact of water 36 wit-hin the vessell with the heating element proper which is the bottom thereof,`

will pass into the interior of the compart-v ments, and the water condensed to be retained within the respective compartments to prevent the main body of water from being flavored by the different foods which may be in the various compartments. A suitable cover 37 is provided for the vessel 16 that may be of any desired heat insulated construction, and leading from the interior of the vessel at the bottom thereof is an outlet 38 with which is connected a faucet 39, see Figure 1.

The solenoids 31 and 32 have a laminated core 40 mounted to slide therein, and said core carries a switch blade 41 for selective engagement with the contacts 42 and 43 to selectively connect the-high and low coils 13 and 14, with the source of electrical supply. The solenoid 31 is formed in two sections or coils 44 and 45, and the solenoid 2 is formed of two sections or coils 46 and 47.

By means of a plug, not shown, the electrical supply line, not shown, is connected with two of four contacts, 1, 2, 3, and 4. The Contact 1 is connected to the switch blade 41 through core 40 ,by a conductor 4S; contact 2 is connected with one end of the coil 45, of solenoid 31, by a conductor 49; contact 3 is connected with one end of coil section 44, of solenoid 31, by a conductor 50; and contact 4 is connected with one end of the high coil 14 by a conductor 51. The other end 4of the high coil 14 is connected with one end of the coil 46 of the solenoid 32 by a conductor 52, and the other end of said coil 46 is connected with one end of the low coil 13 by a conductor 53, the other end of coil 13 being connected withA the switch contact 43 by a conductor 54. The coil 46 of solenoid 32 has a conductor 55 connected therewith, at an inten mediate point, which conductor is connected with the other switch contact 42. The shunt coil 47 of solenoid 32 has one end connected to the main line 51 by a conductor 56, and the. other end of said coil is connected to a spring contact member 57 by a conductor 58. The coil 45 of solenoid 31 also has one end thereof connected to the conductor 51 by a conductor 58 connected with the conductor 56; and the other end of section 44 of solenoid 31 is connected to the conductor 48 by a conductor 44.

Thek core 40 is formed of a number of longitudinally extending laminas, the central one of which is of a width greater than the others t0 provide longitudinally 'extending guides or rails 59. The bottom guide rail 59 runs `or trackswithin the grooves of a pair of guide rollers 60 rotatably mounted upon an insulating base 6l secured to the inner ends of the solenoid spools, as at 62. The central lamina is formed in as at 63, for engagement with the contact- 57 upon the movement of the core from right to left, with reference to Figures 1 and 4. The vcontact 57 is in the form of a spring secured to the base 29, as at 64, and has an insulating block 65 secured on one face thereof to prevent a connection between projection 63 and contact 57 upon movement of the core 40 from left to right, with reference to Figures 1 and 4, but at the same time permitting the connection of said contact and projection upon the reverse move- Vas ment of the core.

The contacts 42 and 43 veach consist of a post 66 carried bythe insulating base 61 to one side of its center and having two spring blades 67 spaced apart a distanceV slightly less than the thickness of blade 41 and having their free ends curved. in opposite directions to guide the blade therebetween. The distance between the extreme inner ends of the contacts 42 and 43 is slightly greater than the width of the switch blade 41 so that said blade moves quickly from one switch clip to the other and said switch clips are of a length sucient to cover the entire width of the switch blade in order to insure a positive connection therewith. The core 40, and with it the switch blade 41, is restrained from wobbling by a guide plate 67 carried by the insulating base 61 and having an elongated slot 68 therein 1n which the extreme outer end `of' the switch blade moves. This guide plate, with the rollers 60, properly support the core without hindrance to its free move- 4ment under action of either of the solenoids 31 and 32.

The general operation' of the heater pro er is, as follows: v

"V' ith the primary coil connected with the source of electrical supply, an induced current is created within the secondary, by the magnetic flux which radiates from the hub 10 through the arms 11 down depending legs 12 and back to the hub throu h the cover 20. In order to out down ed y currents'and excessive `heating within the hub 10, said hub has a slot 69 formed in it.

All the'heat created within our device is quickly utilized by reason of the substance to be heated being in direct contact with the heating element proper and .the latter conducting any heat developed in the primary coils and the magnetic circuit tothe substance to be heated.

The high coil 14 is first connected alone to the supply of electricity. Then when the heating element reaches the desired' temperature, the high coil 14 is connected in series with the low coil 13 when the current consumption is reduced to a value at which the desired temperature of the heating element is maintained. When the core moves to the right, point 63 touches insulating block and so does not make a connection with 57,' and when 41 leaves 42 solenoid 46 is deenergized so that the core moves from 42 to 43 with a snap to prevent arcing, and the low coil is connected in series with the high coil thus cutting down the current. This decreased current however flows through all of solenoid 46, and the number of turns in the left hand part only and in the whole of 46 are so designed that its pull on the core is the same whether the high -current flows through the left hand section or the low current flows through the whole coil. This shift from-the high coil to the low coil in series with the high coil isautomatically performed, by the solenoids 31 and 32 acting upon the core 40 to shift the engagement of the switch blade 41 from contact 42 to contact 43, due to the-drop in current, caused by the increase in resistance df the heating element, causing solenoid 32 to become weaker than 31.

Assuming that the contacts 1 and 4 are in connection with the supply line and the switch blade 41 is engaged between the clip members 67 of the contact '42, the current yflows Jfrom contact 1 through conductor 48, switch blade 41, contact 42, conductor 55, a part of coil" 46, conductor 452, Ahigh coil conductor 51 and then out through contact 4. With the current fiowing as just described, but one art of the series solenoid 46 is energized, an the'pull of this solenoid is greater than that of the shunt solenoid 31 which is shunted across the line by having contacts 2 and 3 connected with each other by thev plug, not shown. As the temperature rises in the secondary, the ow of current through the high co11, and consequently that part of the series solenoid 46 that is energized, decreases, and as the pull of shunt solenoid 31 is constant, the core 41 will be drawn toward the solenoid 31 when the strength of the energized part of solenoid 46 becomes less than that of the shunt solenoid, and the switch blade 41 will the low current rises,

contact 1, through conductor 48, switch l blade 41, contact 43, conductor 54, low coil 13 conductor 53, the entire length of series so enoid coil 46, conductorv52, high coil 14, conductor 51, and then out through contact 4. With the parts in this position, the high and low coils are connected in series and the current consumption reduced to a value at which the heating element proper is maintained at the desired temperature.

When the switch blade 41 leaves contact 43, the series solenoid is disconnected and unless some means were provided the core would snap back to the right under action of the shunt solenoid. Such an occurrence is Splrevented, as after the core has moved a ort distance under action of the series solenoid, but with the blade 41 still engaged between the clips of contact 43, projection 63 makes connection with the spring contact 57. This action connects shunt coil 47 across the conductors 48 and 51 leading from the contacts 1 and 4, respectively, which increases the strength of the series solenoid, and when the switch blade 41 leaves the contact 43, which momentarily renders the series solenoid coil 46 inoperative, the shunt coil 47 of solenoid `32 will be sufficient to move the core 40 to the left with a snap until the switch blade 41 engages contact 42, when part of coil 46 is again energized as the circuit is then with the high coil in connection with the contacts 1 and 4 and the low coil rendered inoperative, as before described.` Instead of connecting solenoid 47, spring contact 57 can be arranged to disconnect shunt solenoid 31 and the inertia of the movement of core 40 will carry switch blade 41 from contact 43 to contact 42.

Movement of the core 40 from right to left continues after the switch blade 41 connects with contact 42 until its limit 'of movement has been-reached, but, before s uch limit of movement is reached, the spring contact slips olf of projection 63 and this renders the shunt coil 47 inoperative. With the parts in this position, the' high coil is on, and when the heating element reaches the desired temperature, the flow of current through the energized section of coil 46 lessens decreasing its strength until it becomes less than that of the constant shunt solenoid, when the core 40 is moved to the right to disconnect high` coil 14 and connect the high and low coil in series, as before described.

When it is desired to have the shift from the high coil to the low and high coil in series take place at another temperature of the heating element, as for instance the boiling point of water, the plug, not shown, can be turned around and 1n that position it connects 3 and 4 together and leaves 2 disconnected from the main line, vwhich connects` section 44 of the .shunt solenoid 31 acrossthe supply line and disconnects '45 thus increasing the strength of said solenoid. As a result of the connecting'of section 44 in the circuit alone, the current liowing through the series solenoid will not decrease to the value required to reduce the pull of the solenoid to a degree less than that of the shunt solenoid when the contact 3 is shorted with contact 2, as the strength of the shunt v solenoid is now nearer the strengthy of the series solenoid when the heater is cold. As the temperature of the heating element proper increases, the current consumption decreases, and when such current consumption reaches the point when the pull of the series solenoid becomes less than the pull of section 44, the core 40 will be moved to the right, in the manner hereinbefore described.

In the event that the temperature of the heating element should drop below the desired heat, the pull of the variable series solenoid will overcome that of the constant shunt solenoid moving the core to the left, in the manner hereinbefore described, to again independently connect the high coil with the electrical supply to raise the heating element to the proper temperature.

It is evident that the means of control described above can also be used to operate magnetic switches or to operate warning signals. A simplerarrangement can be used to operate magnetic switches or signals only when the temperature rises above the desired value or only when it falls below the desired value. Magnets may be used in place of solenoids and springs in place of shunt solenoids. The series solenoid or magnet can be used to kee a buzzer from operating, or hold a manua y operated switch closed against a spring until the current falls to the desiredvalue.

From the foregoin it will be readily ap-l parent to those skille in the art to -which an invention of this character appertalns, that we provide a heating element that is capable of numerous uses, by reason of its novel construction and automatic control, and one which will operate in an entirely satisfactory and eilicie'nt manner. D

What we claim as our invention' 1s: l

l. An electrical heating device, comprlsing a magnetic circuit, a primary coil connectable with a source of electrical supply, and a secondary circuit forming a heaftmg element, said heating element substantlally presenting a con'tinuous integral surface to and being in direct contact with the magnetie` circuit and the substance to be heated.

lll

2. An electrical heating devdce, comprising projecting parte passing around said i arms to link said member with the magnetic circuit, said metal memberand projecting parts forming a secondary, and means for connecting said primary coil with a source of electrical vsupply whereby an induced current is set up in said secondary to raise the temperature thereof.

3. An electricalheater, comprising a magnetic circuit including a member having arms, a primary -coil connectable with a source of electrical supply, and a heating member having parts substantially embracing the arms of the magnetic circuit to conduct heat developed in said magnetic circuit, said heating member forming a secondary circuit.

4. An electrical heater, comprising a magnetic circuit including a member having arms, a primary coil connectable with a source of electrical supply, and a heating member having parts substantially embracing the arms of the magnetic circuit to conduct heat developed in said magnetic circuit and primary coil, said heating member forming a secondary circuit and having an appreciable temperature coeiiicient of resistance, whereby the current consumption ot the heater is decreased as the temperature of the heating element rises.

5. An electrical heater, comprising a magnetic circuit, a primary coil, a secondary Jiorrned of material having a high temperature coeii'cient of resistance whereby the current consumption of the heater is decreased as the temperature of the heating /element rises, said seconda forming a heating element, and means or connecting the primary with a source of electrical sup-` ply whereby an induced current is set up in the secondary which raises the temperature of the heating element.

6. An electrical heater, comp-rising a magnetic circuit, a primary. coil, a secondary formed of'material having a high temperature coeiiicient of resistance whereby the vcurrent consumption of the heater is decreased as the temperature of the heating element rises, said secondary forming a heating element, means for connecting the primary with a source of electrical supply whereby an induced current is set up in the secondary which raises the temperature of the Iheating element, and switch means positioned betweensaid primary and the source of electrical supply and operable automatically upon the rise in temperature of the heating element to a predetermined degree, to change the-primary connections.

7. An electrical heater, comprising a magnetic circuit, -a primary coil, a secondary providing a heating element and formed of material having a high temperature coefficient of resistance, whereby the current consumption of the heaterdecreases as the temperature of the heatinglelement rises; and

momes a switching device between the primary coil and the electrical supply, operable, upon the 8. An electrical heater ofthe class described, comprising a circuit composed of unbroken continuous magnetic metal, a primary coil incased within said circuit, and means for connecting said coil with a source of electrical supply.

9. A device of the class described, comprising a substantially cup shaped member of magnetic material, a secondary linking and in contact with said member, a primary coil enclosed by said member, and a cover of ma etic material vsecured in place while un er pressure and closing the open side of said member.

10. In a device vof the class described, the combination with a heater formed of a primary coil and a secondary circuit connectable with al source of electrical supply, of means whereby the consumption of electrical current by said heater is decreased as4 its temperature rises.

1l. In a device of Ithe class described, the combination with an induced current electrical heating device formed of a primary coil and a secondary circuit connectable with a source of electrical supply, of means for automatically disconnecting said source of electrical supply upon said heating device reaching a predetermined temperature.

12. In a device of the class described, the combination vvitli an induced current electrical heating device formed of a primary coil and a secondary circuit including an electrical circuit, of means for automatically changing said circuit upon a temperature change in said heating device.

13. An electrical heating device including a transformer .heating element having an integral portion which forms the surface-of and is in direct contact with the substance sumption of current changes with a varial tion in the temperature of said secondary, a primary including two coils, means for con-- necting one coil with a source of electrical supply to. induce a current in the secondary, whereby the temperature of said secondary ico les a is rapidlyraised, and means operable by the change of current consumption when the secondary-reaches a predetermined temperature for `disconnecting the ,first coil from the electrical supply and connecting both coils in series and with the supply, to reduce the voltage induced in the secondary and the current flowing in it.

16. A device of the class described, comprising a magnetic circuit, a secondary having a high temperature coefficient of resistance whereby the consumption of current changes with a variation in thetemperature of -said secondary, a primaryA including two coils, means for connecting one of said coils with a source of electrical supply to induce a current in the secondary, whereby the secondary is rapidly heated', means operable by the change of current consumption, when the secondary reaches a predetermined temperature, for disconnecting said coil from the electrical supply and connecting both coils in series and with the supply, and

means operable to reconnect said -iirst mentioned coil with the electrical supply independent of the other coil upon a drop of the temperature of said secondary.

17. A heater of the class described, comprising a magnetic circuit, a primary coil, a secondary of a material having a high temperature coeiiicient of resistance, said secondary forming a heating element, means for connecting the primary, and means for preventing a counter flux within the magnetic circuit. v

18'. An electrical heating device consisting of a primary coil, a welded magnetic circuit and a secondary member, in which said secondary member is in direct contact over a large area, with the insulation on the primary coil, with the magnetic circuit, and with the substance to be heated, said secondary member presenting a continuous integral surface to said substanceto be heated and acting as the secondary circuit; and said magnetic circuit not linking with substance to be heated or passing between primary and any part of secondary circuit.

19. An electrical heating device, comprising a magnetic circuit, a primary coil connectable with a source of electrical supply, a secondary circuit forming a heating element, said heating element substantially presenting a continuous integral surface to and being in 'direct contact with the substance to be heated, and a relatively small air space separating the secondary circuit andthe primary coil at all points.

20. A device of the class described, comprising a primary coil connectable with a source of electrical supply, a welded-magnetic circuit, and a secondary circuit arranged close to said primary coil and magnetic circuit to conduct heat therefrom.

21. In a device of the class described, a primary coil of Wire insulated with a noncomhustible electrical resisting material, a continuous magnetic circuit, said primary coil being retained under pressure and completely surrounded by the magnetic circuit, a closed one-turn distributing secondary formed of the metal of a container composed of a substance having a high temperature coefcient of resistance, means for connecting the primary with a source of electrical supply, and means for automatically controlling the heat generated by the device, said secondary being of irregular thickness in cross section. l

22. A heater of the class described, comprising a magnetic circuit, a primary coil connectable with a source of electrical supply,land a secondary, said primary coil being surrounded by the magnetic circuit and secured in place under pressure.

In testimony whereof, we ax our signatures.

DAVID E. SHAW. HAROLD NICHOLS SHAW. 

